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Studies of Global Stability of Fluid-reversed Configuration Plasmas using a Rigid Body Model

Description: Global stability of field-reversed configuration (FRC) plasmas has been studied using a simple rigid body model in the parameter space ofs (ratio of separatrix radius to average ion gyroradius) and plasma elongation E (ratio of separatrix length to separatrix diameter). Tilt stability is predicted, independent of s, for FRC`s with low E(oblate), while the tilt stability of FRC`s with large E (prolate)depends on s/E. It is found that plasma rotation due to ion diamagnetic drift can stabilize the tilt mode when s/E is less than or equal to1.7. The so-called collisionless ion gyroviscosity also is identified to stabilize tilt when s/E is less than or equal to 2.2. Combining these two effects, the stability regime broadens to s/E is less than or equal to 2.8, consistent with previously developed theories. A small additional rotation (e.g., a Mach number of 0.2) can improve tilt stability significantly at large E. A similar approach is taken to study the physics of the shift stability. It is found that radial shift is unstable when E is < 1 WHILE AXIAL SHIFT IS UNSTABLE WHEN E is> 1. However, unlike tilt stability, gyroviscosity has little effect onshift stability.
Date: April 1998
Creator: Ji, H.
Partner: UNT Libraries Government Documents Department

The Methanosarcina barkeri genome: comparative analysis withMethanosarcina acetivorans and Methanosarcina mazei reveals extensiverearrangement within methanosarcinal genomes

Description: We report here a comparative analysis of the genome sequence of Methanosarcina barkeri with those of Methanosarcina acetivorans and Methanosarcina mazei. All three genomes share a conserved double origin of replication and many gene clusters. M. barkeri is distinguished by having an organization that is well conserved with respect to the other Methanosarcinae in the region proximal to the origin of replication with interspecies gene similarities as high as 95%. However it is disordered and marked by increased transposase frequency and decreased gene synteny and gene density in the proximal semi-genome. Of the 3680 open reading frames in M. barkeri, 678 had paralogs with better than 80% similarity to both M. acetivorans and M. mazei while 128 nonhypothetical orfs were unique (non-paralogous) amongst these species including a complete formate dehydrogenase operon, two genes required for N-acetylmuramic acid synthesis, a 14 gene gas vesicle cluster and a bacterial P450-specific ferredoxin reductase cluster not previously observed or characterized in this genus. A cryptic 36 kbp plasmid sequence was detected in M. barkeri that contains an orc1 gene flanked by a presumptive origin of replication consisting of 38 tandem repeats of a 143 nt motif. Three-way comparison of these genomes reveals differing mechanisms for the accrual of changes. Elongation of the large M. acetivorans is the result of multiple gene-scale insertions and duplications uniformly distributed in that genome, while M. barkeri is characterized by localized inversions associated with the loss of gene content. In contrast, the relatively short M. mazei most closely approximates the ancestral organizational state.
Date: May 19, 2006
Creator: Maeder, Dennis L.; Anderson, Iain; Brettin, Thomas S.; Bruce,David C.; Gilna, Paul; Han, Cliff S. et al.
Partner: UNT Libraries Government Documents Department

The eukaryotic translation elongation factor eEF1A2 induces neoplastic properties and mediates tumorigenic effects of ZNF217 in precursor cells of human ovarian carcinomas

Description: Ovarian epithelial carcinomas (OEC) frequently exhibit amplifications at the 20q13 locus which is the site of several oncogenes, including the eukaryotic elongation factor EEF1A2 and the transcription factor ZNF217. We reported previously that overexpressed ZNF217 induces neoplastic characteristics in precursor cells of OEC. Unexpectedly, ZNF217, which is a transcriptional repressor, enhanced expression of eEF1A2. In this study, array comparative genomic hybridization, single nucleotide polymorphism and Affymetrix analysis of ZNF217-overexpressing cell lines confirmed consistently increased expression of eEF1A2 but not of other oncogenes, and revealed early changes in EEF1A2 gene copy numbers and increased expression at crisis during immortalization. We defined the influence of eEF1A2 overexpression on immortalized ovarian surface epithelial cells, and investigated interrelationships between effects of ZNF217 and eEF1A2 on cellular phenotypes. Lentivirally induced eEF1A2 overexpression caused delayed crisis, apoptosis resistance and increases in serum-independence, saturation densities, and anchorage independence. siRNA to eEF1A2 reversed apoptosis resistance and reduced anchorage independence in eEF1A2-overexpressing lines. Remarkably, siRNA to eEF1A2 was equally efficient in inhibiting both anchorage independence and resistance to apoptosis conferred by ZNF217 overexpression. Our data define neoplastic properties that are caused by eEF1A2 in nontumorigenic ovarian cancer precursor cells, and suggest that eEF1A2 plays a role in mediating ZNF217-induced neoplastic progression.
Date: April 25, 2008
Creator: Sun, Yu; Wong, Nicholas; Guan, Yinghui; Salamanca, Clara M.; Cheng, Jung Chien; Lee, Jonathan M. et al.
Partner: UNT Libraries Government Documents Department

3D analysis of bainite morphologies and kinetics in alloy steels

Description: Serial sectioning and 3D reconstruction of austenite decomposition products were undertaken in bay-forming ternary steels to better understand their true morphologies in the bay region of their TTT diagrams. Jagged growth interfaces are revealed in allotriomorphic bainite formed at the bay in Fe-0.24C-4M0, contrasting with the idealized geometries often assumed when formulating growth models. This also has implications for experimental thickening kinetics measurments. Examination of the so-called 'degenerate' ferrite formed below the bay in Fe-Ox-6.3 W reveals that it is not degenerate at all, but rather has a Widmanstatten rod morphology which gives the appearance of degeneracy due to the multiplicity of ways that they can intersect a randomly-oriented plane of polish. Furthermore, these rods are grouped in packets posessing a common elongation direction, highlighting the crystallographic nature of their formation. The impact of these findings on the understanding of austenite decomposition in bayforming steels will be discussed.
Date: January 1, 2002
Creator: Hackenberg, R. E. (Robert E.); Nordstrom, D. P. (Dale P.) & Shiflet, G. J. (Gary J.)
Partner: UNT Libraries Government Documents Department

Molecular and Genetic Analysis of Hormone-Regulated Differential Cell Elongation in Arabidopsis

Description: The authors have utilized the response of Arabidopsis seedlings to the plant hormone ethylene to identify new genes involved in the regulation of ethylene biosynthesis, perception, signal transduction and differential cell growth. In building a genetic framework for the action of these genes, they developed a molecular model that has facilitated the understanding of the molecular requirements of ethylene for cell elongation processes. The ethylene response pathway in Arabidopsis appears to be primarily linear and is defined by the genes: ETR1, ETR2, ERS1, ERS2, EIN4, CTR1, EIN2, EIN3, EIN5 EIN6, and EIN. Downstream branches identified by the HLS1, EIR1, and AUX1 genes involve interactions with other hormonal (auxin) signals in the process of differential cell elongation in the hypocotyl hook. Cloning and characterization of HLS1 and three HLS1-LIKE genes in the laboratory has been supported under this award. HLS1 is required for differential elongation of cells in the hypocotyl and may act in the establishment of hormone gradients. Also during the award period, they have identified and begun preliminary characterization of two genes that genetically act upstream of the ethylene receptors. ETO1 and RAN1 encode negative regulators of ethylene biosynthesis and signaling respectively. Progress on the analysis of these genes along with HOOKLESS1 is described.
Date: December 3, 2002
Creator: Ecker, Joseph R.
Partner: UNT Libraries Government Documents Department

VLT AND ACS OBSERVATIONS OF RDCS J1252.9-2927: DYNAMICAL STRUCTURE AND GALAXY POPULATIONS IN A MASSIVE CLUSTER AT Z=1.237*

Description: We present results from an extensive spectroscopic survey, carried out with FORS on the ESO Very Large Telescope, and from an extensive multi-wavelength imaging data set from the Advanced Camera for Surveys and ground based facilities of the cluster of galaxies RDCS J1252.9-2927. We have spectroscopically confirmed 38 cluster members in the redshift range 1.22 < z < 1.25. The distribution in velocity of these spectroscopic members yields a cluster median redshift of z = 1.237 and a rest-frame velocity dispersion of 747{sub -84}{sup +74} km s{sup -1}. Star-forming members are observed to mainly populate the outskirts of the cluster while passive galaxies dominate the central cluster region. Using the 38 confirmed redshifts, we were able to resolve, for the first time at z > 1, kinematic structure. The velocity distribution, which is not Gaussian at the 95% confidence level, is consistent with two groups that are also responsible for the projected elongation of the cluster in the East-West direction. The groups are composed of 26 and 12 galaxies and have velocity dispersions of 486{sub -85}{sup +47} km s{sup -1} and 426{sub -105}{sup +57} km s{sup -1}, respectively. The elongation is also seen in the intracluster gas (from X-ray observations) and the dark matter distribution (from a weak lensing analysis). This leads us to conclude that RDCS J1252.9-2927 has not yet reached a final virial state. We extend the analysis of the color-magnitude diagram of spectroscopic members to more than 1 Mpc from the cluster center. The scatter and slope of non-[OII]-emitting cluster members in the near-IR red sequence is similar to that seen in clusters at lower redshift. Furthermore, none of the galaxies with luminosities greater than {approx} K*{sub s} + 1.5 show any [OII] emission feature, indicating that these more luminous, redder galaxies have stopped forming stars earlier ...
Date: March 23, 2007
Creator: Demarco, R; Rosati, P; Lidman, C; Girardi, M; Nonino, M; Rettura, A et al.
Partner: UNT Libraries Government Documents Department

Wheat phytotoxicity from arsenic and cadmium separately and together in solution culture and in a calcareous soil

Description: The toxicity effect of two deleterious elements of arsenic (As) and cadmium (Cd) (individually or in combination) on root elongation of wheat seedlings (Triticum aestivum, L.) were investigated both in hydroponics and in soils freshly spiked with the toxic elements. Median effective concentration (EC{sub 50}) and non-observed effect concentration (NOEC) were used to investigate the toxic thresholds and potencies of the two elements. The EC{sub 50} for As was 0.97 {mu}M in hydroponics and 196 mg {center_dot} kg{sup -1} in soil, and 4.32 {mu}M and 449 mg {center_dot} kg{sup -1} for Cd, respectively. Toxic unit (TU) and additive index (AI) concepts were introduced to determine the combined outcomes, and different behaviors were obtained: synergism in solution culture (EC{sub 50mix} = 0.36 TU{sub mix} and AI: 1.76) and antagonism in soil experiments (EC{sub 50mix} = 1.49 TU{sub mix} and AI: -0.33). Furthermore, the data of soil bioavailable As and Cd can not explain the discrepancy between the results derived from soil and hydroponics experiments.
Date: March 5, 2007
Creator: Cao, Q; Hu, Q; Khan, S; Wang, Z; Lin, A; Du, X et al.
Partner: UNT Libraries Government Documents Department

Effect of Extrusion Temperature on the Microstructural Development of Powder Metallurgy Ti-47A1-2Cr-1Nb-1Ta Alloy

Description: Effect of extrusion temperatures on the microstructural development of a powder metallurgy (PM) Ti-47Al-2Cr-1Nb-1Ta (at. %) alloy has been investigated. Microstructure of the PM alloy extruded at 1150 C consists of a fine-grained ({gamma} + {alpha}{sub 2}) two-phase structure in association with coarse grains of metastable B2 (ordered bcc) phase. In addition, fine {omega} (ordered hexagonal) particles are also found within some B2 grains. The PM alloy containing the metastable B2 grains displays a low-temperature superplastic behavior, in which a tensile elongation of 310% is obtained at 800 C under a strain rate of 2 x 10{sup -5} s{sup -1}. It is suggested that the decomposition of metastable B2 phase and microstructural evolution during the deformation play a crucial role in the low-temperature superplasticity of the PM TiAl alloy. A refined fully-lamellar (FL) microstructure with alternating {gamma} and {alpha}{sub 2} lamellae is developed within the PM alloy extruded at 1400 C. The creep resistance of the refined FL-TiAl alloy is found to be superior to those of the TiAl alloys fabricated by conventional processing techniques. Creep mechanisms for the PM alloy with a refined FL microstructure are critically discussed according to TEM examination of deformation substructure.
Date: June 29, 2000
Creator: Hsiung, L. & Nieh, T.G.
Partner: UNT Libraries Government Documents Department

OPTIMUM PLASMA STATES FOR NEXT STEP TOKAMAKS

Description: OAK A271 OPTIMUM PLASMA STATES FOR NEXT STEP TOKAMAKS. The dependence of the ideal ballooning {beta} limit on aspect ratio, A, and elongation {kappa} is systematically explored for nearly 100% bootstrap current driven tokamak equilibria in a wide range of the shape parameters (A = 1.2-7.0, {kappa} = 1.5-6.0 with triangularity {delta} = 0.5). The critical {beta}{sub N} is shown to be optimal at {kappa} = 3.0-4.0 for all A studied and increases as A decreases with a dependence close to A{sup -0.5}. The results obtained can be used as a theoretical basis for the choice of optimum aspect ratio and elongation of next step burning plasma tokamaks or tokamak reactors.
Date: November 1, 2002
Creator: LIN-LIU,YR & STAMBAUGH,RD
Partner: UNT Libraries Government Documents Department

Enhanced tensile ductility in Al-Mg alloys by solid-solution interactions

Description: The development of methods for obtaining high tensile elongation in aluminum alloys is of great importance for the practical forming of near-net-shape parts. Current superplastic alloys are limited in use by high material costs. The utilization of solute-drag creep processes, the approach used in this study, to obtain enhanced tensile ductility in aluminum alloys has lead to tensile elongations of up to 325% in simple, binary Al-Mg alloys with coarse grain sizes. This method has the advantage of lowering processing costs in comparison with superplastic alloys because a fine grain size is not necessary. Whereas superplastic alloys typically have a strain-rate sensitivity of m = 0.5, the enhanced ductility Al-Mg alloys typically exhibit m = 0.3 where maximum ductility is observed. Although a strain-rate sensitivity of rn = 0.5 can lead to elongations of over 1000% (superplastic materials) a value of m = 0.3 is shown experimentally to be sufficient for obtaining elongations of 150% to a maximum observed of 325%. Enhanced ductility is also affected strongly by ternary alloying additions, such as Mn, for which a preliminary understanding is pursued.
Date: November 29, 1995
Creator: Taleff, E.M.; Henshall, G.A.; Lesuer, D.R.; Nieh, T.G. & Wadsworth, J.
Partner: UNT Libraries Government Documents Department

Development of a Cost-Effective Design for the Fusion Ignition Research Experiment

Description: The Fusion Ignition Research Experiment (FIRE) is one of the components of a US Next Step Options (NSO) study which is considering what major experiments might be undertaken in a restructured US Fusion Sciences Program. FIRE is designed for a plasma current of {approx}6.5 MA, a burn time of at least 10 s, and a Q in the range of 5 to 10. FIRE has a major radius of 2.0 m, a minor radius of 0.525 m, and a field on axis of 10T. All of the coils are inertially cooled by liquid nitrogen. FIRE will operate primarily in a double null configuration with an x-point triangularity of 0.8 and an x-point elongation of 2.2. In addition to these technical requirements, a major goal for the FIRE project is for a total project cost of approximately $1B (in FY 99 dollars). This paper describes the process and rationale for the engineering design chosen for FIRE, taking into account both the performance and cost goals.
Date: December 1, 1999
Creator: Heitzenroeder, Philip J.
Partner: UNT Libraries Government Documents Department

Revision of the tensile database for V-Ti and V-Cr-Ti alloys tested at ANL.

Description: The published database for the tensile properties of unirradiated and irradiated vanadium-based alloys tested at Argonne National Laboratory (ANL) has been reviewed. The alloys tested are in the ranges of V-(0-18)wt.%Ti and V-(4-15)wt.%Cr-(3-15)wt.%Ti. A consistent methodology, based on ASTM terminology and standards, has been used to re-analyze the unpublished load vs. displacement curves for 162 unirradiated samples and 91 irradiated samples to determine revised values for yield strength (YS), ultimate tensile strength (UTS), uniform elongation (UE) and total elongation (TE). The revised data set contains lower values for UE ({minus}5{+-}2% strain) and TE ({minus}4{+-}2% strain) than previously reported. Revised values for YS and UTS are consistent with the previously-published values in that they are within the scatter usually associated with these properties.
Date: January 13, 1998
Creator: Billone, M. C.
Partner: UNT Libraries Government Documents Department

EFFECT OF PROFILES AND SHAPE ON IDEAL STABILITY OF ADVANCED TOKAMAK EQUILIBRIA

Description: OAK-B135 The pressure profile and plasma shape, parameterized by elongation ({kappa}), triangularity ({delta}), and squareness ({zeta}), strongly influence stability. In this study, ideal stability of single null and symmetric, double-null, advanced tokamak (AT) configurations is examined. All the various shapes are bounded by a common envelope and can be realized in the DIII-D tokamak. The calculated AT equilibria are characterized by P{sub 0}/<P> {approx} 2.0-4.5, weak negative central shear, high q{sub min} (> 2.0), high bootstrap fraction, an H-mode pedestal, and varying shape parameters. The pressure profile is modeled by various polynomials together with a hyperbolic tangent pedestal, consistent with experimental observations. Stability is calculated with the DCON code and the resulting stability boundary is corroborated by GATO runs.
Date: August 1, 2003
Creator: MAKOWSKI,MA; CASPER,TA; FERRON,JR; TAYLOR,TS & TURNBULL,AD
Partner: UNT Libraries Government Documents Department

Modelling of Field-Reversed Configuration Experiment with Large Safety Factor

Description: The Translation-Confinement-Sustainment facility has been operated in the 'translation-formation' mode in which a plasma is ejected at high-speed from a {theta}-pinch-like source into a confinement chamber where it settles into a field-reversed-configuration state. Measurements of the poloidal and toroidal field have been the basis of modeling to infer the safety factor. It is found that the edge safety factor exceeds two, and that there is strong forward magnetic shear. The high-q arises because the large elongation compensates for the modest ratio of toroidal-to-poloidal field in the plasma. This is the first known instance of a very high-{beta} plasma with a safety factor greater than unity. Two-fluid modeling of the measurements also indicate several other significant features: a broad 'transition layer' at the plasma boundary with probable line-tying effects, complex high-speed flows, and the appearance of a two-fluid minimum-energy state in the plasma core. All these features may contribute to both the stability and good confinement of the plasma.
Date: November 28, 2005
Creator: Steinhauer, L; Guo, H; Hoffman, A; Ishida, A & Ryutov, D D
Partner: UNT Libraries Government Documents Department

Apple Strength Issues

Description: Strength of the apple parts has been noticed to decrease, especially those installed by the new induction heating system since the LEP campaign started. Fig. 1 shows the ultimate tensile strength (UTS), yield strength (YS), and elongation of the installed or installation-simulated apples on various systems. One can clearly see the mean values of UTS and YS of the post-LEP parts decreased by about 8 ksi and 6 ksi respectively from those of the pre-LEP parts. The slight increase in elongation seen in Fig.1 can be understood from the weak inverse relationship between the strength and elongation in metals. Fig.2 shows the weak correlation between the YS and elongation of the parts listed in Fig. 1. Strength data listed in Figure 1 were re-plotted as histograms in Figs. 3 and 4. Figs. 3a and 4a show histograms of all UTS and YS data. Figs. 3b and 4b shows histograms of pre-LEP data and Figs. 3c and 4c of post-LEP data. Data on statistical scatter of tensile strengths have been rarely published by material suppliers. Instead, only the minimum 'guaranteed' strength data are typically presented. An example of strength distribution of aluminum 7075-T6 sheet material, listed in Fig. 5, show that its scatter width of both UTS and YS for a single sheet can be about 6 ksi and for multi-lot scatter can be as large as 11 ksi even though the sheets have been produced through well-controlled manufacturing process. By approximating the histograms shown in Figs. 3 and 4 by a Gaussian or similar type of distribution curves, one can plausibly see the strength reductions in the later or more recent apples. The pre-LEP data in Figs. 3b and 4b show wider scatter than the post-LEP data in Figs. 3c and 4c and seem to follow the binomial distribution of ...
Date: December 22, 2009
Creator: Syn, C.
Partner: UNT Libraries Government Documents Department

CHARACTERIZATION OF TENSILE STRENGTH OF GLOVEBOX GLOVES

Description: A task was undertaken to compare various properties of different glovebox gloves, having various compositions, for use in gloveboxes at the Savannah River Site (SRS). One aspect of this project was to determine the tensile strength (TS) of the gloves. Longitudinal tensile samples were cut from 15 different gloves and tensile tested. The stress, load, and elongation at failure were determined. All of the gloves that are approved for glovebox use and listed in the glovebox procurement specification met the tensile and elongation requirements. The Viton{reg_sign} compound gloves are not listed in the specification, but exhibited lower tensile strengths than permissible based on the Butyl rubber requirements. Piercan Polyurethane gloves were the thinnest samples and exhibited the highest tensile strength of the materials tested.
Date: February 29, 2012
Creator: Korinko, P. & Chapman, G.
Partner: UNT Libraries Government Documents Department

POWDER METALLURGY TiAl ALLOYS: MICROSTRUCTURES AND PROPERTIES

Description: The microstructures and properties of powder metallurgy TiAl alloys fabricated by hot extrusion of gas-atomized powder at different elevated temperatures were investigated. Microstructure of the alloy fabricated at 1150 C consisted of a mixture of fine ({gamma} + {alpha}{sub 2}) equiaxed grains and coarse ordered B2 grains. Particles of ordered hexagonal {omega} phase were also observed in some B2 grains. The alloy containing B2 grains displayed a low-temperature superplastic behavior: a tensile elongation of 310% was measured when the alloy was tested at 800 C under a strain rate of 2 x 10{sup -5} s{sup -1}. Microstructure of the alloy fabricated at 1250 C consisted of a mixture of fine ({gamma} + {alpha}{sub 2}) equiaxed grains, coarse {alpha}{sub 2} grains, and lamellar ({gamma} + {alpha}{sub 2}) colonies. An observation of stacking faults associated with fine {gamma} lamellae in {alpha}{sub 2} grains reveals that the stacking fault of {alpha}{sub 2} phase plays an important role in the formation of lamellar ({gamma} + {alpha}{sub 2}) colonies. Unlike the alloy fabricated at 1150{sup o}, the alloy fabricated at 1250{sup o} displayed no low-temperature superplasticity, but a tensile elongation of 260% at 1000 C was measured. Microstructure of the alloy fabricated at 1400 C consisted of fully lamellar ({gamma} + {alpha}{sub 2}) colonies with the colony size ranging between 50 {micro}m and 100 {micro}m, in which the width of {gamma} lamella is in a range between 100 nm and 350 nm, and the width of {alpha}{sub 2} lamella is in a range between 10 nm and 50 nm. Creep behavior of the ultrafine lamellar alloy and the effects of alloying addition on the creep resistance of the fully lamellar alloy are also investigated.
Date: December 11, 2006
Creator: Hsiung, L
Partner: UNT Libraries Government Documents Department

Intial synchroscan streak camera imaging at the A0 photoinjector

Description: At the Fermilab A0 photoinjector facility, bunch-length measurements of the laser micropulse and the e-beam micropulse have been done in the past with a single-sweep module of the Hamamatsu C5680 streak camera with an intrinsic shot-to-shot trigger jitter of 10 to 20 ps. We have upgraded the camera system with the synchroscan module tuned to 81.25 MHz to provide synchronous summing capability with less than 1.5-ps FWHM trigger jitter and a phase-locked delay box to provide phase stability of {approx}1 ps over 10s of minutes. This allowed us to measure both the UV laser pulse train at 244 nm and the e-beam via optical transition radiation (OTR). Due to the low electron beam energies and OTR signals, we typically summed over 50 micropulses with 1 nC per micropulse. We also did electron beam bunch length vs. micropulse charge measurements to identify a significant e-beam micropulse elongation from 10 to 30 ps (FWHM) for charges from 1 to 4.6 nC. This effect is attributed to space-charge effects in the PC gun as reproduced by ASTRA calculations. Chromatic temporal dispersion effects in the optics were also characterized and will be reported.
Date: April 1, 2008
Creator: Lumpkin, A. H. & Ruan, J.
Partner: UNT Libraries Government Documents Department

Effect of High-Voltage Heterojunction Bipolar Transistor Collector Design on f(T) and f(MAX)

Description: High-speed InGaP/GaAs heterojunction bipolar transistors (HBTs) for high-voltage circuit applications have been investigated. In order to obtain ideal IV characteristics, a lightly doped (N{sub DC} = 7.5 x 10{sup 15} cm{sup {minus}3}) thick (W{sub C} = 3.5 {micro}m) layer of GaAs was used as the collector layer. The devices fabricated have shown breakdown voltage exceeding 65 V. Device operated at up to a 60V bias, which is the highest operating voltage reported up to date for single heterojunction HBTs. Peak {line_integral}{sub T} and {line_integral}{sub MAX} values of 18 GHz and 29 GHz, respectively, have been achieved on a device with emitter area of 4x 12.5 {micro}m{sup 2}. Both {line_integral}{sub T} and {line_integral}{sub Max} degrades with higher bias, which is related to the elongation of the collector depletion width.
Date: March 2, 1999
Creator: Ashby, C.I.H.; Baca, A.G.; Chang, P.C. & Hietala, V.M.
Partner: UNT Libraries Government Documents Department

Processing and properties of low-aluminum alloy FAPY

Description: This paper deals with the melting, processing, properties, and microstructure of three commercially melted heats of Fe-16 at. % Al alloy FAPY. All of the heats were air-induction melted (AIM), two at Hoskins Manufacturing Company (Hamburg, Michigan) and one at United Defense (Anniston, Alabama). One ingot from each of the heats was used for testing at the Oak Ridge National Laboratory. A 127-mm.-long section from each ingot was used for determining properties and microstructure in the as-cast, cast and hot-processed, and cold-rolled conditions. The fine-grained sheet showed 20% elongation at room temperature.
Date: July 1, 1996
Creator: Sikka, V.K.; Howell, C.R.; Hall, F. & Valykeo, J.
Partner: UNT Libraries Government Documents Department

Structural stability of a rectangular, simply-supported beam subject to a sudden air temperature change next to one surface

Description: For a simply-supported, rectangular beam suddenly heated on one of its surfaces by surrounding air, both elongational and flexural thermal distortions occur. For steel beams of order 10 to 30 cm thick and about 3 m long, flexural displacements, developing in minutes, occur much faster than elongational displacements which occur in hours. The rapid response of the flexural modes is caused by the early-time surface heating of the side of the beam exposed to the suddenly-heated, warmer air. The slower response of the elongation modes is a consequence of a much slower change in the average temperature of the beam. At a span of 3.05 m, the maximum steady state flexural distortions in micrometers were 0.22, 0.78 and 1.56 for respective one-sided air temperature changes in degrees C of 0.28, 1 and 2.
Date: July 3, 1997
Creator: Landram, C. S.
Partner: UNT Libraries Government Documents Department

Flux Consumption Optimization and the Achievement of 1MA Discharge on NSTX

Description: The spherical tokamak (ST), because of its slender central column, has very limited volt-second capability relative to a standard aspect ratio tokamak of similar plasma cross-section. Recent experiments on the National Spherical Torus Experiment (NSTX) have begun to quantify and optimize the ohmic current drive efficiency in a MA-class ST device. Sustainable ramp-rates in excess of 5MA/sec during the current rise phase have been achieved on NSTX, while faster ramps generate significant MHD activity. Discharges with IP exceeding 1MA have been achieved in NSTX with nominal parameters: aspect ratio A=1.3-1.4, elongation k=2-2.2, triangularity d=0.4, internal inductance li=0.6, and Ejima coefficient CE =0.35. Flux consumption efficiency results, performance improvements associated with first boronization, and comparisons to neo-classical resistivity are described.
Date: November 16, 2000
Creator: Menard, J.; LeBlanc, B.; Sabbagh, S.A.; Bell, M.; Bell, R. & al, et
Partner: UNT Libraries Government Documents Department

MECHANICAL PROPERTIES AND MICROSTRUCTURE IN LOW ACTIVATION MARTENSITIC STEELS F82H AND OPTIMAX AFTER 800 MEV PROTON IRRADIATION

Description: Low-activation martensitic steels, F82H (mod.) and Optimax-A, have been irradiated with 800-MeV protons up to 5.9 dpa. The tensile properties and microstructure have been studied. The results show that radiation hardening increases continuously with irradiation dose. F82H has lesser irradiation hardening as compared to Optimax-A in the present work and DIN1.4926 from a previous study. The irradiation embrittlement effects are evident in the materials since the uniform elongation is reduced sharply to less than 2%. However, all the irradiated samples ruptured in a ductile-fracture mode. Defect clusters have been observed. The size and the density of defect clusters increase with the irradiation dose. Precipitates are amorphous after irradiation.
Date: October 1, 1999
Creator: DAI, Y. & AL, ET
Partner: UNT Libraries Government Documents Department

Numerical Study of Global Stability of Oblate Field-Reversed Configurations

Description: Global stability of the oblate (small elongation, E < 1) Field-Reversed Configuration (FRC) has been investigated numerically using both three-dimensional magnetohydrodynamic (MHD) and hybrid (fluid electrons and kinetic ions) simulations. For every non-zero value of the toroidal mode number n, there are three MHD modes that must be stabilized. For n = 1, these are the interchange, the tilt and the radial shift; while for n > 1 these are the interchange and two co-interchange modes with different polarization. It is shown that the n = 1 tilt mode becomes an external mode when E < 1, and it can be effectively stabilized by close-fitting conducting shells, even in the small Larmor radii (MHD) regime. The tilt mode stability improves with increasing oblateness, however at suffciently small elongations the radial shift mode becomes more unstable than the tilt mode. The interchange mode stability is strongly profile dependent, and all n * 1 interchange modes can be stabilized for a class of pressure profile with separatrix beta larger than 0.035. Our results show that all three n = 1 modes can be stabilized in the MHD regime, but the stabilization of the n > 1 co-interchange modes still remains an open question.
Date: October 27, 2000
Creator: Belova, E.V.; Jardin, S.C.; Ji, H.; Yamada, M. & Kulsrud, R.
Partner: UNT Libraries Government Documents Department